It is particularly preferred to employ Staphylococcal genes and gene products as targets for the development of antibiotics. The Staphylococci make up a medically important genera of microbes. They are known to produce two types of disease, invasive and toxigenic. Invasive infections are characterized generally by abscess formation effecting both skin surfaces and deep tissues. S. aureus is the second leading cause of bacteremia in cancer patients. Osteomyelitis, septic arthritis, septic thrombophlebitis and acute bacterial endocarditis are also relatively common. There are at least three clinical conditions resulting from the toxigenic properties of Staphylococci. The manifestation of these diseases result from the actions of exotoxins as opposed to tissue invasion and bacteremia. These conditions include: Staphylococcal food poisoning, scalded skin syndrome and toxic shock syndrome.
The frequency of Staphylococcus aureus infections has risen dramatically in the past 20 years. This has been attributed to the emergence of multiply antibiotic resistant strains and an increasing population of people with weakened immune systems. It is no longer uncommon to isolate Staphylococcus aureus strains which are resistant to some or all of the standard antibiotics. This has created a demand for both new anti-microbial agents and diagnostic tests for this organism.
Arginine deiminase has been shown to function in protecting bacterial cells against the damaging effects of acid environments. For example, as little as 2.9 mM arginine added to acidified suspensions of Streptococcus sanguis at a pH of 4.0 resulted in ammonia production and protection against killing (see Casiano-Colon A, Marquis R E., [1988] Appl Environ Microbiol 54(6):1318-1324). Also, bacteria have been found to be able to utilize L-arginine as the energy source for growth under anaerobic, nitrate-free conditions using arginine deiminase enzyme (see Luthi E, Mercenier A, Haas D. [1986] J Gen Microbiol 132(Pt 10):2667-2675). Consequently, the enzyme encoded by the arginine deiminase gene is a target for novel antibacterial screening to find agents which would hinder the development of the disease state by a bacterial pathogen by preventing its adaptation to acidic environments or hindering its ability to produce sufficient energy for the maintenance of infection in the hostile environment presented by the host.
Substantial effort has been invested this century in the successful discovery and development of antibacterials. Paradoxically, although antibacterials are devised to eradicate infection in mammals, we know almost nothing of the physiology of bacterial pathogens in infective situations in the host. Using sequences from the Staphylococcus aureus chromosome, we have developed an RT-PCR based procedure which allows us to identify those bacterial genes transcribed at any stage of infection and also from different niches of infection. The derivation of such information is a critical first step in understanding the global response of the bacterial gene complement to the host environment. From the knowledge of bacterial genes, both of known and unknown function which are widely transcribed in the host, it is possible to attempt to ascertain by database searching those which are present only in the eubacteria. Further prioritisation of such genes, by consideration of the likely role of their products towards the maintenance of infection and the facility of setting up a screen for inhibitors of the biochemical function indicated by their homology to characterised genes, allows the compilation of a shortlist for gene essentiality studies using genetic deletion or controlled regulation techniques. The proteins expressed by genes shown to be necessary for growth in vitro or in pathogenesis in animal models provide novel targets for antibacterial screening to find agents which are broadly inhibitory towards pathogenesis. This invention provides S.aureus WCUH 29 polynucleotides which are transcribed in infected tissue, in particular in both acute and chronic infections.
Clearly, there is a need for factors, such as the novel compounds of the invention, that have a present benefit of being useful to screen compounds for antibiotic activity. Such factors are also useful to determine their role in pathogenesis of infection, dysfunction and disease. There is also a need for identification and characterization of such factors and their antagonists and agonists which can play a role in preventing, ameliorating or correcting infections, dysfunctions or diseases.
The polypeptides of the invention have amino acid sequence homology to a known protein, namely arcA of Clostridium perfringens. See GeneBank Accession Number X97684.